A PCR-BASED METHOD TO CHARACTERIZE AND IDENTIFY BENZIMIDAZOLE RESISTANCE IN HELMINTHOSPORIUM-SOLANI

Control of Helminthosporium solani, the cause of silver scurf in potat o tubers, has been impaired by selection of benzimidazole-resistant st rains as a result of repeated use of the fungicide thiabendazole. Iden tification of thiabendazole-resistant strains of H. solani by conventi onal techniques takes several weeks. Primers designed from conserved r egions of the fungal beta-tubulin gene were used to PCR amplify and se quence a portion of the gene. A point mutation was detected at codon 1 98 in thiabendazole-resistant isolates causing a change in the amino a cid sequence from glutamic acid to alanine or glutamine. Species-speci fic PCR primers designed to amplify this region were used in conjuncti on with a restriction endonuclease to cause cleavage in sensitive isol ates only and thus provide a rapid diagnostic test to differentiate fi eld isolates.